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GCSE Chemistry 03 — Chemical Changes

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Topics include Reactivity series & displacement reactions, Electrolysis: ions, electrodes and products, Acids, bases, salts and neutralisation, Titration calculations (moles and concentration), and Placeholder concept (auto-added for schema compliance).

Chemistry EN
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Electrolysis: ions, electrodes and products

Electrolysis decomposes ionic substances using electricity. Predicting products depends on which ions are present and where they move.

Key points

  • Electrolysis needs an electrolyte (molten or aqueous ionic).
  • Cations go to the cathode (−) and gain electrons (reduction).
  • Anions go to the anode (+) and lose electrons (oxidation).
  • Molten salts: products come only from the salt’s ions.
  • Aqueous solutions: water ions can compete.

Worked example

Question

Predict products for molten PbBr2\text{PbBr}_2 electrolysis.

Solution

Ions: Pb2+\text{Pb}^{2+}, Br−\text{Br}^-.
Cathode: Pb2++2e−→Pb\text{Pb}^{2+} + 2e^- \to \text{Pb}.
Anode: 2Br−→Br2+2e−2\text{Br}^- \to \text{Br}_2 + 2e^-.
Answer: Cathode: lead. Anode: bromine.

Common pitfalls

  • Reversing electrode charges.
  • Forgetting OILRIG.
  • Treating aqueous and molten cases the same.

Prerequisites

  • Prerequisite knowledge (auto-added).
  • Prerequisite knowledge (auto-added).
Further resources